1. Field of the Invention
This invention relates to a serial-parallel type analog-to-digital (A/D) converter.
2. Description of the Prior Art
A typical prior art serial-parallel type A/D converter includes higher-order and lower-order A/D converting sections, a digital-to-analog (D/A) converting section, and a subtracter. The higher-order A/D converting section roughly converts an analog input signal into a corresponding digital signal which constitutes a higher-order part of a final digital signal. The digital output signal from the higher-order A/D converting section is converted back into a corresponding analog signal by the D/A converting section. The subtracter executes the subtraction between the input analog signal and the analog output signal from the D/A converting section, and amplifies the resultant difference between the two analog signals. The lower-order A/D converting section converts the analog output signal from the subtracter into a corresponding digital signal which constitutes a lower-order part of the final digital signal. The digital output signals from the higher-order and lower-order A/D converting sections are combined to form the final digital signal.
In the above-mentioned prior-art serial-parallel type A/D converter, it is necessary to accurately set various parameters such as the gain of the subtracter, the full-scale voltage of the lower-order A/D converting section, and the offset voltage of the D/A converting section. In order to realize the accurate setting of these parameters, many adjustment points are provided. The large number of the adjustment points tends to decrease the stability in the conversion accuracy. In addition, it is generally difficult to form the prior art A/D converter by a monolithic IC (integrated circuit).